class_docstr: A kernel that takes nested structures as inputs.
  
  The inputs are flattened and concatenated, and then passed to the base kernel.
code: def kernel(self):
      return self._kernel
  
file_path: probability/tensorflow_probability/python/math/psd_kernels/internal/test_util.py
imports: import tensorflow.compat.v2
  from tensorflow_probability.python.internal import parameter_properties
  from tensorflow_probability.python.internal import prefer_static
  from tensorflow_probability.python.math.psd_kernels import positive_semidefinite_kernel
label_desc: Use image node_id 3 for calling the MultipartTestKernel obj's underlying member method code with example usage: obj.kernel() and returns: self